A heavy-duty belt-type conveyor for transporting bulk material mainly underground along a closed path traversing at least one loading or unloading zone is known which has a track on the path and including a main rail following the path outside the zone and having ends at the zone, respective intersections at the zone connected between the rail ends and respective right and left rail branches extending between the intersections. An endless conveyor belt extends along the path and through the zone and has right and left longitudinal edges provided with respective endless rows of longitudinally spaced right and left trucks alternating with one another along the path and each having a lower end attached to the respective belt edge and an upper end riding on and displaceable longitudinally in the rail. An endless and flexible tension-transmitting drive element extends along the path and through the zone and is connected at least indirectly to the belt and trucks. A drive is connected to the drive element for advancing the belt and trucks along the path in a transport direction. Relative to the transport direction, at the upstream intersection the right trucks pass into the right branch and the left trucks into the left branch. The belt is closed and tubular outside the zone when its right and left trucks are all in the main rail and is open in the zone when the right trucks are in the right branch and the left trucks are spaced therefrom in the left branch. The rails can be rigid, or can even be cables (see Foerdern und Heben, 1954, p. 571, FIG. 12).
With this system it is therefore possible to load material onto the open belt at the zone or unload it therefrom, but outside the zone or zones the belt is closed. When thus closed it occupies minimal space and the normally dusty bulk material is enclosed. The belt can be provided with internal transverse partitions so it can even move vertically.
Such a system, as described in West German Pat. No. 965,024 as well as in East German Pat. No. 11,632, can have trucks each provided with a main lower roller that rides on the main rail outside the zone. The trucks attached to the one edge, for example the left edge, are also each provided above the main roller with a separate deflection roller. At the intersection at the upstream end of the loading or unloading zone the left branch has an input end positioned above the main rail to catch and engage these upper rollers. The main rail is constructed to permit the main rollers of the left trucks to move at the upstream and downstream intersections transversely between the main rail and the left branch. The main rail extends continuously through the zone to form the right branch while the upper left branch diverges from it and converges with it. Plainly such mechanism is relatively complex and failure-prone. When for some reason a left truck does not catch, the belt does not open so it cannot unload or be loaded.
A conveyor of this general type is also known, as for example from Foerdern und Heben (1962 page 640) or from commonly assigned copending U.S. patent application No. 385,065 filed June 4, 1982, which has a plurality of guides carrying an endless conveyor belt having a horizontal intake stretch, a vertical transport stretch following the intake stretch, a horizontal output stretch following the transport stretch, and a return stretch extending from the output stretch to the intake stretch. Drive means is connected to the edges for advancing the belt in a transport direction from the intake stretch through the transport stretch to the output stretch and then back through the return stretch to the intake stretch. Closing means at the intake stretch moves the belt edges from a spaced-apart position with the belt open therebetween to a juxtaposed position with the belt tubular. Thus the belt is tubular as it enters the transport stretch. Opening means at the output stretch moves the belt edges from the juxtaposed position to the spaced-apart position. Thus the belt is flattened out at the output stretch. Bulk material loaded onto the flattened-out belt in the intake station is transported by the belt through the vertical stretch and discharged from the belt at the output stretch.
In such a system the belt edges are joined and separated like a slide fastener so they very securely surround the bulk material being transported and allow the belt to work even perfectly vertically, to which end the belt has internal transverse partitions to prevent the load from slipping back down inside itself.
A relatively foolproof belt-type conveyor is also described in German patent application No. H 18,736 SI/81e which has separate and endless right and left rails that are immediately adjacent each other outside the loading and unloading zones, but that are separated at these zones. Such a system is quite expensive to make and maintain due to the duplication of parts, although it normally can be counted on to work well.